(CNN) -- The fiance of a top Brazilian model -- whose hands and feet were amputated in a bid to save her from a deadly and little-known illness -- said he believes she will wake up from a coma, noting, "where there is a heartbeat, there is hope."

Brazilian model Mariana Bridi is in a serious condition after undergoing multiple amputations.

Mariana Bridi da Costa, 20, was in "very critical condition" on Friday, doctors said, as she fought a pernicious disease that has ravaged her body and forced doctors to perform the amputations and extract part of her stomach as well as both kidneys.

She was breathing through a respirator, officials at Dorio Silva Hospital in the Brazilian state of Espirito Santo said Friday.

"Where there is a heartbeat, there is hope," her fiance, Thiago Simoes, told CNN in a telephone interview.

Da Costa suffered from necrosis, or the fast deadening of tissue, caused by septicemia.

Septicemia, triggered by a bacterial infection, causes insufficient blood flow that can lead to organ failure.

Bridi first sought medical advice after feeling ill in late December. Hospital officials said she was transferred to Dorio Silva on January 3 in "septic shock," a serious medical condition caused by an inflammation.

Bridi was first diagnosed as suffering a urinary tract infection. By the time the infection was detected, it had developed into septicemia.

Doctors decided to amputate first her hands and then her feet after the condition reduced the amount of oxygen being delivered to her limbs.

Dr. Charles Clarke, honorary consultant neurologist for the National Hospital for Neurology and Neurosurgery in the United Kingdom, said the development of a urinary tract infection to septicemia requiring amputation was "very rare."

Just less than one month ago, Bridi was a healthy young woman well on the way to achieving her dream of becoming a world class model.

She placed sixth in the Miss Bikini International competition in China last year and took first place for the "Best in Swimsuit" category. In 2007 and 2008, she came fourth in the contest to become Brazil's entrant for the Miss World pageant.

Simoes said da Costa was on her way to international stardom, signing with prominent model scout Dilson Stein, who brought Brazilian models, including Gisele Bundchen and Luize Altenhofen, to the world stage.

"All the agencies were very interested in knowing her. I know for a fact that they would have loved her because Mariana is beautiful," Stein told Brazil's Tribuna newspaper.

Her fiance told CNN that da Costa woke up from a coma ten days ago and told him how much she wanted to be alive.

"She told me she was praying to stay alive, that she still had a lot to do on this earth, that she wanted to go on with her plans," he said.

"She comes from a humble family and she was the main breadwinner," said Simoes, who refuted rumors that da Costa was dieting and that might have affected her health.

"She never dieted, never took pills...she is a very simple, very warm human being," he said.

Meanwhile, Tribuna reporter Rafaele Gasparini, who recently spent several hours with da Costa's family, told CNN that they were not so optimistic about her condition, which is deteriorating rapidly.

"Her father told me that she is unconscious and her blood pressure is dropping rapidly," said Gasparini.

"Her relatives walked out (in the afternoon), and there seemed to be a farewell mood," she said.

Gasparini said the model was in a "forced coma," which might help her body recover from the physical shock. She was also being treated with noradrenaline. Known as a "fight or flight" chemical that the body releases in stressful situations, noradrenaline produces increased blood pressure and heart rate.

A doctor who recently published an article in The New England Journal of Medicine on the disease, told CNN that little was known about the illness, although it is the tenth leading cause of deaths in the United States.

"We know a lot about what happens once a patient contracts the illness but we know very little about what causes it," said Dr. Greg Martin of Emory University in Atlanta.

"It is a leading health threat in this country, killing at least 800,000 people a year," he said.

Martin said sepsis was a "response" to an infection, which can cause the immune system to lose its balance.

"Basically, the immune system goes haywire after contracting an infection and begins to overreact," he said.

Men were more susceptible than women, Martin said.

News of Bridi's condition spread quickly throughout Brazil and then worldwide. A message on her Web site said the volume of traffic had caused it to crash, and that the site had received more than 15,000 hits in two days.

"The whole world, I repeat, the whole world is touched by the case of Mariana," it said.

The message said they had received "e-mails of solidarity from all corners of the world: Australia, Ukraine, Czech Republic, France, Italy, USA, Russia, etc."

The model's family and friends have urged people to keep praying for her survival. "Mariana is (a) warrior and will win this battle," they said in a statement.